The present invention is generally directed to toner compositions and processes for the preparation thereof, and more specifically to toner compositions and chemical preparative processes for directly generating silane-modified toner particles of small particle size and narrow particle size distribution without resorting to conventional pulverization and classification methods. In one embodiment, the present invention relates to processes for preparing small sized spherical toner particles comprised of a polymer resin or resins, and colorants comprising color pigments, dyes, or mixtures thereof, dispersed homogeneously or substantially homogeneously throughout the polymer resin or resins, and wherein the toner has been coated with a layer of a cellulose derivative component generated from the reaction of a suitable silane reagent with the cellulose molecules on the toner's surface. The silane modification of the cellulose surface layer enhances the toner's powder flow characteristics, and eliminates or substantially reduces the toner's sensitivity to humidity changes.
The toner particles of the present invention can be prepared in embodiments by a simple one-pot process which comprises (1) forming a stable oil-in-water microdroplet suspension by dispersing with high sheer blending a mixture of addition monomers, free radical initiators, colorants, and optional preformed polymers in an aqueous cellulose surfactant solution containing an optional inorganic surfactant; (2) converting the microdroplets into polymer toner particles by polymerizing the addition monomers via free radical polymerization; and (3) treating the resulting toner particles with suitable silane reagents, affording the silane-modified toner particles of the present invention. It is believed that during the dispersion step, the cellulose surfactant molecules adsorb and precipitate on the microdroplets, forming a thin microcapsule coating around the microdroplets. The cellulose surface coating inhibits the droplet-to-droplet coalescence, and enables the attainment of narrow droplet size distributions. The encapsulation of microdroplets by the cellulose surfactant molecules also facilitates subsequent free radical polymerization without the complications of suspension failure which is commonly observed in suspension polymerization. Also, the silane-modified cellulose shell renders the toners of the present invention relatively hydrophobic, and they are therefore in embodiments not sensitive, or substantially insensitive to changes in relative humidity. In addition, the silane-modified cellulose shell can serve to protect the toner components such as polymer resins and colorants, thereby isolating them from the adverse effects of their environment. Another attribute of the protective silane-modified cellulose coating relates to the complete, or substantially complete nullification or passivation of the charging effects of colorants present in the toners. Accordingly, for two-component development where toner particles are admixed with carrier particles, the triboelectric properties of toners are thereby controlled or substantially dominated by the charging effects of the outer silane-modified cellulose coating. The passivation of the charging effects of colorants is particularly important for multi-color xerography, since similar or substantially similar equilibrium triboelectric characteristics can be readily achieved with these toners regardless of the nature of the colorants present in the toners. For single component development where triboelectric charging is generally accomplished by a frictional charging blade, similar equilibrium triboelectric charge levels can also be obtained with different colored toners of the present invention under identical, or substantially similar conditions. Furthermore, effective containment of the toner components enabled by the silane-modified cellulose coating of the present invention prevents these components from leaching to the toner's surface, thereby eliminating or substantially reducing the problem of toner blocking or agglomeration in toners wherein, for example, toner resins of low glass transition temperatures are utilized.
In color reprography, such as in full color or highlight color processes, colored toners with a wide variety of colors including black are usually employed. For two-component development, it is highly desirable that the triboelectric properties of different colored toners be controlled, thereby permitting them to attain similar equilibrium triboelectric charging levels when utilized with the same carriers. This is especially useful for custom colored toner packages which can be generated by the simple blending of the primary colored toners of the present invention. Another important aspect of two-component development is the rate of charging of fresh, substantially uncharged toners to equilibrium charge levels when added to the toner depleted development housing. A fast rate of charging of fresh toners is important in ensuring proper image development, particularly for high speed reprographic systems. These and other advantages are achieved with the toners of the present invention.
Colorants such as color pigments or dyes have a dominant effect on the triboelectric charging behavior of toners as the colorants are often present at or close to the surface of the toner, and are, therefore, exposed to the environment. As a consequence, when the toner particles are admixed with carriers, the interactions of the exposed pigments of the toners with the carrier particles can affect, and often dominate the charging behavior of the toner. This can also occur for a number of prior art encapsulated toners where the color pigment particles are not completely encapsulated within the toner shell. Accordingly, toners with identical, or substantially similar components, but different colorants, often exhibit different charging behavior, sometimes to the extent of achieving triboelectric charges of opposite polarity. To overcome this difficulty, it is usually necessary to utilize different triboelectric charge control additives for different colorants or to incorporate a high level of charge control additives into the toner to nullify or overcome the different charging effects of different colorants. The toners of the present invention eliminate or substantially overcome this difficulty. As a consequence, the need to rely on different or high levels of charge control additives for different colored toners for achieving similar triboelectric charging levels is eliminated or substantially avoided with the toners and processes of the present invention.
Encapsulated toners and processes are known. For example, both U.S. Pat. No. 4,626,489 and British Patent 1,538,787 disclose processes for the preparation of colored encapsulated toners wherein both the core resin and shell materials are prepared by suspension polymerization techniques. U.S. Pat. No. 4,565,764 discloses a colored microcapsule toner comprised of a colored core encapsulated by two resin shells with the inner shell having an affinity for both the core and the outer shell; and U.S. Pat. No. 4,254,201 illustrates the use of pressure sensitive toner clusters or aggregates with each granule of the cluster or aggregate being comprised of a pressure sensitive adhesive substance encapsulated by coating film. Color pigment particles or magnetic particles can be present on the surfaces of the encapsulated granules to impart the desired color to the toners. Also, U.S. Pat. No. 4,727,011 discloses a process for preparing encapsulated toners which involves a shell forming interfacial polycondensation and a core binder forming free radical polymerization, and further U.S. Pat. No. 4,708,924 discloses the use of a mixture of two polymers, one having a glass transition temperature in the range of -90.degree. C. to 5.degree. C., and the other having a softening temperature in the range of 25.degree. C. to 180.degree. C., as the core binders for a pressure fixable encapsulated toner. Other prior art, all United States patents, are summarized below: No. 4,339,518, which relates to a process of electrostatic printing with fluorinated polymer toner additives where suitable materials for the dielectric toner include thermoplastic silicone resins and fluorine containing resins having low surface energy, reference column 4, beginning at line 10, note for example the disclosure in column 4, line 16, through column 6; No. 4,016,099, which discloses methods of forming encapsulated toner particles and wherein there are selected organic polymers including homopolymers and copolymers such as vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene, and the like, see column 6, beginning at line 3, wherein there can be selected as the core materials polyolefins, polytetrafluoroethylene, polyethylene oxide and the like, see column 3, beginning at around line 18, No. 4,265,994 directed to pressure fixable capsule toners with polyolefins, such as polytetrafluoroethylene, see for example column 3, beginning at line 15; No. 4,497,885, which discloses a pressure fixable microcapsule toner comprising a pressure fixable component, a magnetic material, and other optional components, and wherein the core material can contain a soft material, typical examples of which include polyvinylidene fluoride, polybutadiene, and the like, see column 3, beginning at line 10; No. 4,520,091 which discloses an encapsulated toner with a core which comprises a colorant, a dissolving solvent, a nondissolving liquid and a polymer, and may include additives such as a fluorine containing resin, see column 10, beginning at line 27; No. 4,590,142 relating to capsule toners wherein additives such as polytetrafluoroethylenes are selected as lubricating components, see column 5, beginning at line 52; and Nos. 4,599,289 and 4,803,144.
With further specific reference to the prior art, there are disclosed in U.S. Pat. No. 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there are disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes are also selected for the preparation of the toners of this patent. Also, there are disclosed in the prior art encapsulated toner compositions containing costly pigments and dyes, reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483.
In a search report, there were located the following United States Patents as being of background interest and relating to the treatment of colloidal silica with silane coupling agents Nos. 3,720,617; 3,819,367; 3,983,045 and 4,868,084; and 4,565,758 which discloses the inclusion of a silane coupling agent in a photoreceptor.
The disclosures of all the United States patents and other patent documents mentioned herein are totally incorporated herein by reference.
A number of patents and copending applications illustrate various encapsulated toner compositions including, for example, U.S. Pat. No. 5,043,240, U.S. Pat. No. 5,035,970, U.S. Pat. No. 5,037,716, U.S. Pat. No. 5,045,428, U.S. Pat. No. 5,013,630, U.S. Pat. No. 5,023,159, U.S. Ser. No. 516,864, U.S. Pat. No. 5,077,167, U.S. Ser. No. 456,278, U.S. Pat. No. 5,114,819, U.S. Pat. No. 5,082,757, and U.S. Ser. No. 617,222, the disclosures of each of the aforementioned patents and copending applications being totally incorporated herein by reference.